THE BEARERS OF THE HERITAGE 



313 



Maturation of the egg-cell. — As regards the behavior of the 

 chromosomes the maturation of the ovum parallels that of the sperm- 

 cell. There are not so many primordial germ-cells formed and only 

 one out of four of the ultimate cells becomes a functional egg. As in 

 maturation of the sperm-cell there is a growth period in which o'dgonia 

 enlarge to become primary oocytes (Fig. 48, b). In each primary 



spermatogenesis 



1 





Secondary ( ^\ 



•ipermocd-K *^ } 



Ci/ttS VJx 



Sperm- 



Oogenesis 



1 



Multiphcalion Period 



Croh/th Period 



] 



Pairing of Chromosomes 

 j fiec/ucing dii/mon 



^@ 



Oogonia 



Pnmary dlc^li 



Sec one/ari/ cdci/t» 

 ip^um and first 

 ■~ polar do</jf) 



I jr^rtoiure onurri 



Qnti polor b9</l'tj 



/ /,' ) ^'^"ft >yum 



fuitnumber of 

 <hroFno:,omti 

 reilored 



Fig. 49. — Diagram showing the parallel between maturation of the sperm- 

 cell and maturation of the ovum. {From Guyer.) 



oocyte as in the primary spermatocyte the chromosomes pair and two 

 rapidly succeeding divisions follow in one of which the typical numeri- 

 cal reduction in the chromosomes occurs. A peculiarity in the 

 maturation of the ovum is that there is a very unequal division in 

 the cytoplasm in cell-division so that three of the resulting cells 

 usually termed polar bodies are very small and appear like minute 

 buds on the side of the fourth or egg-cell proper. 



